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TB or not TB: an answer to the culling question

Culling for TB kills 6,000 badgers a year, but a vaccination pilot scheme could eliminate the disease in cattle without harming the native Irish mammal

Thu, Apr 11, 2013, 06:00

Anthony King

A vaccination pilot programme under way could save thousands of Irish badgers and eventually eliminate bovine tuberculosis (TB) from this native mammal.

A field trial to test the BCG vaccine in wild badgers has seen scientists catch, tag and vaccinate hundreds in Co Kilkenny over the past three years.

“The vaccine is aimed at eradicating the disease in the badger, so if you have a TB-free badger population then you can’t get transmission from badgers to cattle,” explains Dr Eamonn Gormley, a veterinary scientist in University College Dublin involved in this project.

When badgers are implicated in TB outbreaks in cattle herds their numbers are suppressed locally, with the result that over 6,000 Irish badgers are culled each year.

“As an interim solution it is quite effective at reducing transmission from badgers to cattle,” says Gormley, though it will not eliminate the disease unless you cull all badgers. “It’s a protected species and no one wants to do that.”

The Irish Wildlife Trust describes culling as inhumane. Today there are between 50,000 and 90,000 badgers here, culling having removed tens of thousands over the last decade. “We would push for the vaccine as soon as possible,” says Fintan Kelly at the trust. “Culling is the worst option. We don’t even know how many badgers we have.”

Tests with the vaccine have been carried out in captured animals for over a decade. In Kilkenny the vaccine is squirted into the mouths of sedated badgers. For the future it is hoped badgers will self-vaccinate by eating bait containing the BCG vaccine. Perhaps 80 per cent of badgers would need to be vaccinated in order for the strategy to succeed.

Levels of TB halved in cattle over the last four years, says James O’Keefe, head of the wildlife unit in the Department of Agriculture. He says farmers are happy with the TB programme, but he is hoping they can be shown that vaccination is effective or better than culling.

“Shooting a badger is not a nice thing to have to do and it is costly as the animal then has to be transported for disposal,” he says. The Kilkenny trial – involving twice-yearly captures of badgers – looks promising so far.

Ireland’s bovine TB programme costs taxpayers around €60 million each year, part of a TB-control effort that began in the 1950s. Gormley says there was a gradual realisation that the problem in cattle would never be solved without addressing TB in badgers.

Badgers transmit bovine TB to each other and cattle mainly through air. “You only need a small dose. One single bacillus is sufficient to set up an infection [in the lungs],” explains Gormley.

Scottish scientists recently reported evidence from DNA studies of direct transmission of the TB bacteria between cattle and badgers at the farm level.

It will be several years before the oral bait is ready for widespread use, according to the department. However research is crucial to get the bait to the right place at the right time, with scientists at Trinity College Dublin assisting here.

“They love the bait. The main problem is working out whether it is the boss badger eating all the bait,” says Trinity zoologist Dr Nicola Marples.

Ideally, vaccine pellets could be placed close to where they routinely forage and flavoured with peanut butter or molasses, which badgers love. “Results so far are encouraging and you can get quite high coverage rates of all members of the badger population when you put out baits for about four to five days,” says Gormley.

Irish badgers often build their setts in hedgerows, unlike their British counterparts which favour woodland, and so live close to pastures.

Badgers will eat small mammals and birds. “If you were a hedgehog your badger is your worst nightmare,” says O’Keefe. “A badger will flick them with a paw onto their bellies and whip them open.”

“Talk about making do with what is around you, they wrote that book,” says O’Keefe. “They are a wonderful animal and I have come to respect them hugely over the years.”

Rabies was eliminated from European foxes using baited vaccine. Similar success with the BCG vaccine in badgers could see national programmes in both Ireland and the UK, which are jointly shouldering the research effort.

Results from the Kilkenny trial are expected in six to nine months. Irish experts say success in a national vaccine programme will take many years. The aim will be to gradually increase the number of TB-free badger populations until the disease can be cornered and eliminated.

IRISH BADGERS: A separate subspecies
Irish badgers are more closely related to Spanish and Scandinavian than British badgers, according to a recent DNA study by Denise O’Meara of Waterford Institute of Technology.

She says the Irish badger has a unique and interesting genetic history and that culling large numbers to prevent the spread of TB is removing some of that genetic history.

Her research on badger DNA bolstered its credentials for being an Irish native. “There are so many differences between Irish and UK badgers,” says Dr Nicola Marples of Trinity College Dublin. “I believe they may be a separate subspecies.”

UK badgers tend to eat lots of earthworms. Mediterranean badgers favour fruits and berries. Irish badgers are different. In spring and autumn they root around the topsoil for beetles and other insects, but will focus on moth larvae when available.

In summer, bees and wasp nests and lots of frogs are consumed, says Marples. During winter they spend more time in their underground tunnels (setts) and don’t eat much from the surface.

A study of hundreds of badgers’ stomach contents also revealed that Irish badgers eat lots of rough vegetation, surprising given that their carnivore gut can’t digest this material. Irish badgers live in smaller social groups than UK animals and tend to wander around the countryside a great deal more. They are also less territorially combative, suffering far fewer bite wounds than UK badgers.

What they do share is their distinct striped markings, which may be a warning to potential adversaries. The warning relates to an incredibly powerful, bone-splitting bite.

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